Signal responsive relay system



Aug. 1941- J. s. LEIGH 2,252,084

SIGNAL RESRONSIVE RELAY SYSTEM Filed March 30, 1940 Snventor Jab azagmeg Patented Aug. 12, 1941 SIGNAL RESPONSIVE RELAY SYSTEM John S. Leigh,Pennsauken, N. J., assignor to Radio Corporation of America, acorporation of Delaware Application March 30, 1940, Serial No. 327,046

4 Claims.

This invention relates to signal responsive relay systems for actuatingcontrol apparatus in re sponse to applied signals, and has for itsprimary object to provide a relay system of the character referred towhich is highly sensitive and which may be connected with a signalsupply circuit without causing distortion of signals therein.

It is also an object of the present invention to provide a signalresponsive relay system for radio signal circuits and the like, which isof simplified and low cost construction and which imposes a negligibleload on the system in operation.

A relay system embodying the invention is particularly adapted for usein connection with audio frequency signal transmission circuitsproviding for muting or silencing the output therefrom, in the absenceof received signals. However, the system may be employed for the controlof any circuit and includes a highly sensitive rectifier deviceproviding a uniform and substantially negligible load on the signalsupply circuit and a relay device having suitable control contacts.

ihe invention will, however, be better understood from the followingdescription, when considered in connection with the accompanyingdrawing, and its scope is pointed out in the appended claims.

In the drawing,

Figure 1 is a schematic circuit diagram of a signal amplifier andcontrol means therefor embodying, the invention, and

Figures 2 and 3 are graphs showing curves illustrating operatingfeatures of the circuit of Fig. 1.

Referring to Fig. l, 5 and low potential leads of a signal conveyingchannel 1 comprising suitable amplifying apparatus 8 and 9 and a signaloutput device, such as a loudspeaker l0. The amplifiers 8 and 9 may beconnected by a suitable circuit indicated by leads and I2 correspondingto leads 5 and 6, and providing a continuation of the signal channelthrough the two amplifying portions 8 and 9.

The amplifying portion 9, representing any suitable portion of thesignal channel which may be controlled, is provided with a circuitcomprising leads I3 for modifying the signal output of the channel inany suitable manner, such as by muting or cutting off the signal outputentirely or reducing it to a sub-normal value when the circuit I3 isclosed or opened. In the present example, it may be assumed that whenthe circuit I3 is closed, as by means of relay contacts indicated at [4and E5, the signal channel is normally operative to convey signals fromthe leads 5 and 6 are the high and 6 through to the loudspeaker devicel0, and that when the circuit I3 is open, as by opening the contacts l4and I5, the signal channel is inoperative, or reduced in effectiveness,to produce signals at the loudspeaker I0.

The relay contacts M and I5 are controlled by a relay coil l6 connectedin the output circuit I! of a detector or signal rectifier I8, whichreceives signal energy from the signal channel I at any suitable point,such as between the amplifier sections 8 and S in connection with theleads I and i2. This signal energy is applied to the tube l8 through astep-up audio frequency transformer 20 providing a relatively highstep-up ratio between the primary winding 2| and the secondary winding22.

The primary winding 2| is connected through leads 23 with the signalchannel across the circuit at H and I2 and may include a filter deviceor other control element 25, hereinafter referred to, between theprimary winding 2| and the leads I ||2.

The detector I8 may be of any suitable type comprising a cathode 26, asignal input grid 21, and an output anode 28 connected with the outputcircuit H. The transformer secondary 22 is connected between the cathodeand the grid 21 through a grid leak resistor 29 and a grid capacitor 30,whereby grid rectification takes place in response to signals andproviding a negative bias on the grid 21 proportional to the signalstrength.

The resulting anode current supplied from suitable terminals 32connected between the relay l6 and a cathode lead 33, varies inaccordance with the curve 35 shown in Fig. 2, assuming a maximum valuein the absence of signals and falling to a lower Value as the signalstrength is increased. It will be noted that this change in anodecurrent requires a relatively wide change in signal strength and theanode current change is relatively low.

By applying an initial positive bias to the grid 21 from the positive Bsupply circuit through a controlling resistor 36 which is preferablyvariable as shown, a. higher degree of sensitivity may be obtainedwithout effecting the loading of the primary 2| and the signal conveyingcircuit. The variation in anode current of the detector |8 with apredetermined positive bias applied to the grid 21 is indicated by thecurve 31 in Fig. 2 and, as will be noted, the anode current varies overa relatively wide range with a relatively small change in input signalamplitude, making the system highly sensitive and providing a change inoperating current through the relay coil 15, which actuates the contacts[4, i5 in response to a slight signal.

However, this is made possible by the fact that the step-up ratio of thetransformer 28 from the primary 2| to the secondary 22 and the gridcircuit of the tube is such that with a very low amplitude signal in thechannel at H-l2 corresponding to a slight signal voltage at 5-5,sufficient voltage is applied to the signal grid 21 to bias the tube 21substantially to cut-off as ind cated by the curve 31,

The step-up ratio of the transformer, therefore, is dependent upon theoperating characteristics of the tube employed and the amplification inthe signal channel preceding the circuit I [-1 2, and the arrangement issuch that, in any case, a relatively small change in signal amplitude atthe input circuit 5-5 is sufficient to cause the anode current of thetube to fall from a relatively high value established by the controlresistor and the biasing potential applied therethrough, andsubstantially zero anode current.

In the present example, therefore, the relay i6 is arranged to permitthe contacts l4l5 to be held open in the absence of signals and to closein the presence of even a slight signal, thereby placing the channel inoperation.

In a preferred application of the invention, the element 25 in the inputcircuit of the transformer is a band pass or low pass filter permittingvoice currents in a predetermined range to actuate the relay, therebypermitting speech to be transmitted through the channel l, 22 from theterminals 5, 6 and to exclude all other signals and to render the systemimmune from noise by muting the output in the absence of the desiredsignals. It is obvious, however, that the contacts I i, I5 may beutilized to control any suitable circuit and that the element in theinput circuit may be omitted or may be utilized to control the responseof the system in any suitable manner.

The operation of the tube l8 in response to sig nals and the control ofthe positive bias may be understood more clearly from a consideration ofFig. 3, wherein the curve 33 is the grid current curve of the tube andthe curve 38 is the plate current curve, drawn to different scales, thenormal zero signal plate current being indicated at the point to on thecurve 39, while the zero -signal plate current with positive bias, isindicated at the point M on the curve 39.

It has been found that this system and mode of operation of therectifier provides a highly responsive control; that is, it is quicklyresponsive to apply signals and causes no appreciable distortion of thesignals through the channel H, 2 for the reason that it providessubstantially light and constant load over the signal cycle.Fiuthermore, it is relatively simple in arrangement and involves circuitelements which are of relatively low cost, including the transformer 20which may be of small size, since it is not utilized to convey anyappreciable power, but is required only to provide a high voltagestep-up between the signal channel and the rectifier IS.

A visual indication of the change in anode current as an indication ofthe strength of the applied signals may be provided by a suitablecurrent responsive device in the anode circuit i? such as an indicatingmeter 45, a by-pass capacitor 46 being provided to shunt the said meter,and the potential supply source 32, as indicated.

The regulation of the resistor 36 is relatively poor in operation,causing a drop in potential as the grid current tends to increase andwith a triode detector, as shown, may have a value of 220,000 ohms. Asuitable grid leak and capacitor for audio frequency currents comprisesa resistor of substantially 5.4 megohms at 29 and a capacitor of .1 mid.at 30.

I claim as my invention:

1. A signal responsive control system compris ing, in combination, asignal supply circuit including a step-up transformer having arelatively high step-up ratio, a rectifier device having a signal inputgrid-cathode circuit including the secondary of said transformer, meansproviding a negative bias source for said last named circuit in responseto signals and through said transformer a load on said supply circuitwhich is relatively low and substantially uniform over each signalcycle, an output anode circuit for said rectifier device including acontrol device responsive to changes in anode current, and means forapplying a positive bias potential across said input circuit, therelation of said biasing potential and the step-up ratio of saidtransformer being such that a relatively wide range of variation in theanode current is effected by a relatively small change in signalamplitude applied to said input circuit.

2. The combination with a signal amplifying channel, of a step-uptransformer having a primary winding and a secondary winding providing arelatively high step-up ratio, means for applying signals to saidprimary winding from said channel, a control tube having a grid circuitconnected with said secondary winding and a source of negative biasingpotential responsive to applied signals, said circuit providing arelatively light and substantially constant load on said signal channelwith said relatively high step-up ratio for said transformer, meansincluding a series regulating resistor for applying a predeterminedinitial positive bias potential to said grid circuit, and meansproviding an output anode circuit responsive to variations in anodecurrent.

3. The combination with a signal amplifying channel, of a step-uptransformer having a primary winding and a secondary winding providing arelatively high step-up ratio, means for applying signals to saidprimary winding from said channel, a control tube having a grid circuitconnected with said secondary winding including a grid leak and a gridcapacitor providing a negative bias potential source therein in responseto signals, said circuit impedance providing a relatively light andsubstantially constant load on said signal channel with said relativelyhigh stepup ratio for said transformer, means including a seriesregulating resistor for applying a predetermined initial positivebiasing potential to said grid circuit, means providing an output anodecircuit for said control tube responsive to variations in anode current,and means controlled by said current variations for impairing the signaltransmission through said channel.

4. The combination with a signal transmission channel, of a transformerhaving a primary winding connected with said channel to receiveamplified signals therefrom, a detector having a grid, a cathode and anoutput anode, an output anode circuit connected between said anode andsaid cathode, means for supplying anode current to said circuit, asecondary for said transformer connected between said grid and cathode,a grid leak and a shunt grid capacitor therefor serially included incircuit between said secondary and the grid of said tube, a bias supplycircuit including a series resistor connected with said grid forapplying thereto a positive potential with normal value, and saidtransformer having a step-up ratio providing a signal voltage from saidchannel of an amplitude to reduce said anode current substantially tozero in response to sigrespect to the cathode whereby the zero signal 5nals of a predetermined low amplitude.

anode current of said tube is increased above a JOHN S. LEIGH.

